McGinn gained 8 percent from a similar poll in March that had him tied with former King County Executive Ron Sims for the lead at 15 percent, followed by Seattle City Councilmember Tim Burgess with 10 percent. But Sims decided not to enter the race. Burgess dropped out last Friday.

While McGinn's camp can argue the latest poll shows him gaining support, other political observers say the numbers are so soft, he will struggle just to make it out of the primary.

Erica. C. Barnett with Publicola, points out McGinn has less support than incumbent mayor Greg Nickels had in a similar poll before ultimately losing in an eight-way primary in 2009.